Hi Tu-fpt
The only place where I saw the limitations on the routing-instances was in the Advanced VPNs guide (training book)
It was said there that on M and T series in V5.6 ( ??? Quite very old I admit) you have to stay under 2000 VRF tables.
With less that 200 routes in each one (if you use OSPF)
Another combination given is 100 VRF with 1000 static routes in each.
The document wasn't more precise (If you folowed this training it's in the chapter Advanced VPN scaling L3 VPN)
In fact it will depend a lot and on a lot of things:
- routing protocol used in the Routing-instance
- Number of routes in there
- Number of interfaces
- ...
I hope someone from Juniper could give you some more precise answer .
HTH